1. Field of the Invention
The present invention relates to a process for preparation of one or more metallic oxide thin layers on a substrate which provides improved surface properties and improved stabilization of these layers, and to the layered structures formed thereby.
2. Discussion of the Background
The use of vacuum deposition techniques is known to provide thin layer systems which are often inadequate with respect to their mechanical and chemical behavior. These inadequacies are observed particularly in systems which comprise one or several layers of an n-type semi-conductor metallic oxide, such as tin-oxide-based layers. One cause for such increased sensitivity of the surface layers can be found in the use of a reactive cathodic sputtering process (also known as cathodic pulverization) when the ratio of argon and oxygen in the reaction gas exceeds a certain value or when the gases contain traces of water or hydrocarbon. Such contamination cannot always be avoided in industrial installations.
It is known that the mechanical or chemical behavior of thin layer systems can be improved with the aid of a stabilization treatment. In DD-B-272 971, a process for stabilization of the surface metallic oxide layer by means of air treatment with oxygen-saturated water is described. The improvement in performance thus obtained is thought to occur through the depletion of interstitial oxygen molecules in the surface oxide layer.
In accordance with another known process described in DD-B-281 819, thin layer systems comprising an oxide as a surface layer are stabilized by means of a treatment in aqueous solutions of chromates, dichromates or permanganates. Here, again, the improvement in performance of the layer systems is accounted for by an oxygen depletion of the surface layer.